kubernetes 实战5_命令_Assign Pods to Nodes&Configure a Pod to Use a ConfigMap

Assign Pods to Nodes

how to assign a Kubernetes Pod to a particular node in a Kubernetes cluster.

Add a label to a node

#List the nodes in your cluster:
kubectl get nodes

#The output is similar to this:
NAME      STATUS    AGE     VERSION
worker0   Ready     1d      v1.6.0+fff5156
worker1   Ready     1d      v1.6.0+fff5156
worker2   Ready     1d      v1.6.0+fff5156

#chose one of your nodes, and add a label to it:
#where <your-node-name> is the name of your chosen node.
kubectl label nodes <your-node-name> disktype=ssd

#Verify that your chosen node has a disktype=ssd label:
kubectl get nodes –show-labels

#The output is similar to this:
#In the preceding output, you can see that the worker0 node has a disktype=ssd label.
NAME      STATUS    AGE     VERSION            LABELS
worker0   Ready     1d      v1.6.0+fff5156     ...,disktype=ssd,kubernetes.io/hostname=worker0
worker1   Ready     1d      v1.6.0+fff5156     ...,kubernetes.io/hostname=worker1
worker2   Ready     1d      v1.6.0+fff5156     ...,kubernetes.io/hostname=worker2

Create a pod that gets scheduled to your chosen node

#List the nodes in your cluster
kubectl get nodes

#The output is similar to this
NAME      STATUS    AGE     VERSION
worker0   Ready     1d      v1.6.0+fff5156
worker1   Ready     1d      v1.6.0+fff5156
worker2   Ready     1d      v1.6.0+fff5156

#Chose one of your nodes, and add a label to it
#where <your-node-name> is the name of your chosen node.
kubectl label nodes <your-node-name> disktype=ssd

#Verify that your chosen node has a disktype=ssd label:
kubectl get nodes –show-labels

#The output is similar to this
NAME      STATUS    AGE     VERSION            LABELS
worker0   Ready     1d      v1.6.0+fff5156     ...,disktype=ssd,kubernetes.io/hostname=worker0
worker1   Ready     1d      v1.6.0+fff5156     ...,kubernetes.io/hostname=worker1
worker2   Ready     1d      v1.6.0+fff5156     ...,kubernetes.io/hostname=worker2

#In the preceding output, you can see that the worker0 node has a disktype=ssd label.

　　

Create a pod that gets scheduled to your chosen node

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    env: test
spec:
  containers:
  - name: nginx
    image: nginx
    imagePullPolicy: IfNotPresent
  nodeSelector:
    disktype: ssd

　　

This pod configuration file describes a pod that has a node selector, disktype: ssd.

This means that the pod will get scheduled on a node that has a disktype=ssd label.

#Use the configuration file to create a pod that will get scheduled on your chosen node:
kubectl create -f https://k8s.io/docs/tasks/configure-pod-container/pod.yaml

#Verify that the pod is running on your chosen node:
kubectl get pods --output=wide

#The output is similar to this:
NAME     READY     STATUS    RESTARTS   AGE    IP           NODE
nginx    1/1       Running   0          13s    10.200.0.4   worker0

　　

Configure Pod Initialization

how to use an Init Container to initialize a Pod before an application Container runs.

Create a Pod that has an Init Container

apiVersion: v1
kind: Pod
metadata:
  name: init-demo
spec:
  containers:
  - name: nginx
    image: nginx
    ports:
    - containerPort: 80
    volumeMounts:
    - name: workdir
      mountPath: /usr/share/nginx/html
  # These containers are run during pod initialization
  initContainers:
  - name: install
    image: busybox
    command:
    - wget
    - "-O"
    - "/work-dir/index.html"
    - http://kubernetes.io
    volumeMounts:
    - name: workdir
      mountPath: "/work-dir"
  dnsPolicy: Default
  volumes:
  - name: workdir
    emptyDir: {}

　　

In this exercise you create a Pod that has one application Container and one Init Container.

The init container runs to completion before the application container starts.

In the configuration file, you can see that the Pod has a Volume that the init container and the application container share.

The init container mounts the shared Volume at /work-dir,

and the application container mounts the shared Volume at /usr/share/nginx/html.

The init container runs the following command and then terminates:

wget -O /work-dir/index.html http://kubernetes.io

Notice that the init container writes the index.html file in the root directory of the nginx server.

#Create the Pod:
kubectl create -f https://k8s.io/docs/tasks/configure-pod-container/init-containers.yaml

#Verify that the nginx container is running:
kubectl get pod init-demo

#The output shows that the nginx container is running:
NAME        READY     STATUS    RESTARTS   AGE
init-demo   1/1       Running   0          1m

#Get a shell into the nginx container running in the init-demo Pod:
kubectl exec -it init-demo -- /bin/bash

#In your shell, send a GET request to the nginx server:
root@nginx:~# apt-get update
root@nginx:~# apt-get install curl
root@nginx:~# curl localhost

#The output shows that nginx is serving the web page that was written by the init container:
<!Doctype html>
<html id="home">

<head>
...
"url": "http://kubernetes.io/"}</script>
</head>
<body>
  ...
  <p>Kubernetes is open source giving you the freedom to take advantage ...</p>
  ...

　　

　

Attach Handlers to Container Lifecycle Events

how to attach handlers to Container lifecycle events.

Kubernetes supports the postStart and preStop events.

Kubernetes sends the postStart event immediately after a Container is started,

and it sends the preStop event immediately before the Container is terminated.

Define postStart and preStop handlers

apiVersion: v1
kind: Pod
metadata:
  name: lifecycle-demo
spec:
  containers:
  - name: lifecycle-demo-container
    image: nginx
    lifecycle:
      postStart:
        exec:
          command: ["/bin/sh", "-c", "echo Hello from the postStart handler > /usr/share/message"]
      preStop:
        exec:
          command: ["/usr/sbin/nginx","-s","quit"]

　　

In this exercise, you create a Pod that has one Container.

The Container has handlers for the postStart and preStop events.

In the configuration file, you can see that the postStart command writes a message file to the Container’s /usr/share directory.

The preStop command shuts down nginx gracefully.

This is helpful if the Container is being terminated because of a failure.

#Create the Pod:
kubectl create -f https://k8s.io/docs/tasks/configure-pod-container/lifecycle-events.yaml

#Verify that the Container in the Pod is running:
kubectl get pod lifecycle-demo

#Get a shell into the Container running in your Pod:
kubectl exec -it lifecycle-demo -- /bin/bash

#In your shell, verify that the postStart handler created the message file:
root@lifecycle-demo:/# cat /usr/share/message

#The output shows the text written by the postStart handler:
Hello from the postStart handler

　　

Kubernetes sends the postStart event immediately after the Container is created.

There is no guarantee, however, that the postStart handler is called before the Container’s entrypoint is called.

The postStart handler runs asynchronously relative to the Container’s code, but Kubernetes’ management of the container blocks until the postStart handler completes.

The Container’s status is not set to RUNNING until the postStart handler completes.

Kubernetes sends the preStop event immediately before the Container is terminated.

Kubernetes’ management of the Container blocks until the preStop handler completes, unless the Pod’s grace period expires.

For more details, see Termination of Pods.

Note:

Kubernetes only sends the preStop event when a Pod is terminated.

This means that the preStop hook is not invoked when the Pod is completed.

This limitation is tracked in issue #55087.

Configure a Pod to Use a ConfigMap

ConfigMaps allow you to decouple configuration artifacts from image content to keep containerized applications portable.

This page provides a series of usage examples demonstrating how to create ConfigMaps and configure Pods using data stored in ConfigMaps.

Create a ConfigMap

#Use the kubectl create configmap command to create configmaps from directories, files, or literal values:
kubectl create configmap <map-name> <data-source>
#<map-name> is the name you want to assign to the ConfigMap
#<data-source> is the directory, file, or literal value to draw the data from.

　　

The data source corresponds to a key-value pair in the ConfigMap, where

• key = the file name or the key you provided on the command line, and
• value = the file contents or the literal value you provided on the command line.

You can use kubectl describe or kubectl get to retrieve information about a ConfigMap.

Create ConfigMaps from directories

You can use kubectl create configmap to create a ConfigMap from multiple files in the same directory.

mkdir -p configure-pod-container/configmap/kubectl/

wget https://k8s.io/docs/tasks/configure-pod-container/configmap/kubectl/game.properties -o configure-pod-container/configmap/kubectl/game.properties

wget https://k8s.io/docs/tasks/configure-pod-container/configmap/kubectl/ui.properties -o configure-pod-container/configmap/kubectl/ui.properties

kubectl create configmap game-config --from-file=configure-pod-container/configmap/kubectl/

#combines the contents of the configure-pod-container/configmap/kubectl/
ls configure-pod-container/configmap/kubectl/
game.properties
ui.properties

#into the following ConfigMap:

kubectl describe configmaps game-config
Name:           game-config
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
game.properties:        158 bytes
ui.properties:          83 bytes

　　

The game.properties and ui.properties files in the configure-pod-container/configmap/kubectl/ directory are represented in the data section of the ConfigMap.

kubectl get configmaps game-config -o yaml

apiVersion: v1
data:
  game.properties: |
    enemies=aliens
    lives=3
    enemies.cheat=true
    enemies.cheat.level=noGoodRotten
    secret.code.passphrase=UUDDLRLRBABAS
    secret.code.allowed=true
    secret.code.lives=30
  ui.properties: |
    color.good=purple
    color.bad=yellow
    allow.textmode=true
    how.nice.to.look=fairlyNice
kind: ConfigMap
metadata:
  creationTimestamp: 2016-02-18T18:52:05Z
  name: game-config
  namespace: default
  resourceVersion: "516"
  selfLink: /api/v1/namespaces/default/configmaps/game-config
  uid: b4952dc3-d670-11e5-8cd0-68f728db1985

　　

Create ConfigMaps from files

You can use kubectl create configmap to create a ConfigMap from an individual file, or from multiple files.

kubectl create configmap game-config-2 --from-file=configure-pod-container/configmap/kubectl/game.properties

kubectl describe configmaps game-config-2

Name:           game-config-2
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
game.properties:        158 bytes

You can pass in the --from-file argument multiple times to create a ConfigMap from multiple data sources.

kubectl create configmap game-config-2 --from-file=configure-pod-container/configmap/kubectl/game.properties --from-file=configure-pod-container/configmap/kubectl/ui.properties

kubectl describe configmaps game-config-2

Name:           game-config-2
Namespace:      default
Labels:         <none>
Annotations:    <none>

Data
====
game.properties:        158 bytes
ui.properties:          83 bytes

　　

Use the option --from-env-file to create a ConfigMap from an env-file:

# Env-files contain a list of environment variables.
# These syntax rules apply:
#   Each line in an env file has to be in VAR=VAL format.
#   Lines beginning with # (i.e. comments) are ignored.
#   Blank lines are ignored.
#   There is no special handling of quotation marks (i.e. they will be part of the ConfigMap value)).

wget https://k8s.io/docs/tasks/configure-pod-container/configmap/kubectl/game-env-file.properties -o configure-pod-container/configmap/kubectl/game-env-file.properties

cat configure-pod-container/configmap/kubectl/game-env-file.properties

enemies=aliens
lives=3
allowed="true"

# This comment and the empty line above it are ignored

kubectl create configmap game-config-env-file \
        --from-env-file=configure-pod-container/configmap/kubectl/game-env-file.properties

kubectl get configmap game-config-env-file -o yaml

apiVersion: v1
data:
  allowed: '"true"'
  enemies: aliens
  lives: "3"
kind: ConfigMap
metadata:
  creationTimestamp: 2017-12-27T18:36:28Z
  name: game-config-env-file
  namespace: default
  resourceVersion: "809965"
  selfLink: /api/v1/namespaces/default/configmaps/game-config-env-file
  uid: d9d1ca5b-eb34-11e7-887b-42010a8002b8

　　

When passing --from-env-file multiple times to create a ConfigMap from multiple data sources, only the last env-file is used:

wget https://k8s.io/docs/tasks/configure-pod-container/configmap/kubectl/ui-env-file.properties -o configure-pod-container/configmap/kubectl/ui-env-file.properties
kubectl create configmap config-multi-env-files \
        --from-env-file=configure-pod-container/configmap/kubectl/game-env-file.properties \
        --from-env-file=configure-pod-container/configmap/kubectl/ui-env-file.properties

kubectl get configmap config-multi-env-files -o yaml

apiVersion: v1
data:
  color: purple
  how: fairlyNice
  textmode: "true"
kind: ConfigMap
metadata:
  creationTimestamp: 2017-12-27T18:38:34Z
  name: config-multi-env-files
  namespace: default
  resourceVersion: "810136"
  selfLink: /api/v1/namespaces/default/configmaps/config-multi-env-files
  uid: 252c4572-eb35-11e7-887b-42010a8002b8

　　

Define the key to use when creating a ConfigMap from a file

You can define a key other than the file name to use in the data section of your ConfigMap when using the --from-file argument:

kubectl create configmap game-config-3 --from-file=<my-key-name>=<path-to-file>

　　where <my-key-name> is the key you want to use in the ConfigMap

　　and <path-to-file> is the location of the data source file you want the key to represent.

kubectl create configmap game-config-3 --from-file=game-special-key=configure-pod-container/configmap/kubectl/game.properties

kubectl get configmaps game-config-3 -o yaml

apiVersion: v1
data:
  game-special-key: |
    enemies=aliens
    lives=3
    enemies.cheat=true
    enemies.cheat.level=noGoodRotten
    secret.code.passphrase=UUDDLRLRBABAS
    secret.code.allowed=true
    secret.code.lives=30
kind: ConfigMap
metadata:
  creationTimestamp: 2016-02-18T18:54:22Z
  name: game-config-3
  namespace: default
  resourceVersion: "530"
  selfLink: /api/v1/namespaces/default/configmaps/game-config-3
  uid: 05f8da22-d671-11e5-8cd0-68f728db1985

　　

Create ConfigMaps from literal values

You can use kubectl create configmap with the --from-literal argument to define a literal value from the command line:

kubectl create configmap special-config --from-literal=special.how=very --from-literal=special.type=charm

　　

You can pass in multiple key-value pairs.

Each pair provided on the command line is represented as a separate entry in the data section of the ConfigMap.

kubectl get configmaps special-config -o yaml

apiVersion: v1
data:
  special.how: very
  special.type: charm
kind: ConfigMap
metadata:
  creationTimestamp: 2016-02-18T19:14:38Z
  name: special-config
  namespace: default
  resourceVersion: "651"
  selfLink: /api/v1/namespaces/default/configmaps/special-config
  uid: dadce046-d673-11e5-8cd0-68f728db1985

　　

Define Pod environment variables using ConfigMap data

Define a Pod environment variable with data from a single ConfigMap

#Define an environment variable as a key-value pair in a ConfigMap:
kubectl create configmap special-config --from-literal=special.how=very 

#Assign the special.how value defined in the ConfigMap to the SPECIAL_LEVEL_KEY environment variable in the Pod specification.
kubectl edit pod dapi-test-pod

apiVersion: v1
   kind: Pod
   metadata:
     name: dapi-test-pod
   spec:
     containers:
       - name: test-container
         image: k8s.gcr.io/busybox
         command: [ "/bin/sh", "-c", "env" ]
         env:
           # Define the environment variable
           - name: SPECIAL_LEVEL_KEY
             valueFrom:
               configMapKeyRef:
                 # The ConfigMap containing the value you want to assign to SPECIAL_LEVEL_KEY
                 name: special-config
                 # Specify the key associated with the value
                 key: special.how
     restartPolicy: Never

#Save the changes to the Pod specification. Now, the Pod’s output includes SPECIAL_LEVEL_KEY=very.

　　

Define Pod environment variables with data from multiple ConfigMaps

#As with the previous example, create the ConfigMaps first.

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: special-config
     namespace: default
   data:
     special.how: very

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: env-config
     namespace: default
   data:
     log_level: INFO

#Define the environment variables in the Pod specification.
apiVersion: v1
   kind: Pod
   metadata:
     name: dapi-test-pod
   spec:
     containers:
       - name: test-container
         image: k8s.gcr.io/busybox
         command: [ "/bin/sh", "-c", "env" ]
         env:
           - name: SPECIAL_LEVEL_KEY
             valueFrom:
               configMapKeyRef:
                 name: special-config
                 key: special.how
           - name: LOG_LEVEL
             valueFrom:
               configMapKeyRef:
                 name: env-config
                 key: log_level
     restartPolicy: Never

#Save the changes to the Pod specification. Now, the Pod’s output includes SPECIAL_LEVEL_KEY=very and LOG_LEVEL=info

　　

Configure all key-value pairs in a ConfigMap as Pod environment variables

Note: This functionality is available to users running Kubernetes v1.6 and later.

#Create a ConfigMap containing multiple key-value pairs.

   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: special-config
     namespace: default
   data:
     SPECIAL_LEVEL: very
     SPECIAL_TYPE: charm

#Use envFrom to define all of the ConfigMap’s data as Pod environment variables.
#The key from the ConfigMap becomes the environment variable name in the Pod. 

 apiVersion: v1
   kind: Pod
   metadata:
     name: dapi-test-pod
   spec:
     containers:
       - name: test-container
         image: k8s.gcr.io/busybox
         command: [ "/bin/sh", "-c", "env" ]
         envFrom:
         - configMapRef:
             name: special-config
     restartPolicy: Never

#Save the changes to the Pod specification. Now, the Pod’s output includes SPECIAL_LEVEL=very and SPECIAL_TYPE=charm.

　　

Use ConfigMap-defined environment variables in Pod commands

You can use ConfigMap-defined environment variables in the command section of the Pod specification using the $(VAR_NAME) Kubernetes substitution syntax.

apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "echo $(SPECIAL_LEVEL_KEY) $(SPECIAL_TYPE_KEY)" ]
      env:
        - name: SPECIAL_LEVEL_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: SPECIAL_LEVEL
        - name: SPECIAL_TYPE_KEY
          valueFrom:
            configMapKeyRef:
              name: special-config
              key: SPECIAL_TYPE
  restartPolicy: Never

　　

produces the following output in the test-container container:

very charm

　　

Add ConfigMap data to a Volume

As explained in Create ConfigMaps from files,

when you create a ConfigMap using --from-file, the filename becomes a key stored in the data section of the ConfigMap.

The file contents become the key’s value.

apiVersion: v1
kind: ConfigMap
metadata:
  name: special-config
  namespace: default
data:
  special.level: very
  special.type: charm

　　

Populate a Volume with data stored in a ConfigMap

Add the ConfigMap name under the volumes section of the Pod specification.

This adds the ConfigMap data to the directory specified as volumeMounts.mountPath (in this case, /etc/config).

The command section references the special.level item stored in the ConfigMap.

apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh", "-c", "ls /etc/config/" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        # Provide the name of the ConfigMap containing the files you want
        # to add to the container
        name: special-config
  restartPolicy: Never

When the pod runs, the command ("ls /etc/config/") produces the output below:

special.level
special.type

Caution: If there are some files in the /etc/config/ directory, they will be deleted.

Add ConfigMap data to a specific path in the Volume　　

Use the path field to specify the desired file path for specific ConfigMap items.

In this case, the special.level item will be mounted in the config-volume volume at /etc/config/keys.

apiVersion: v1
kind: Pod
metadata:
  name: dapi-test-pod
spec:
  containers:
    - name: test-container
      image: k8s.gcr.io/busybox
      command: [ "/bin/sh","-c","cat /etc/config/keys" ]
      volumeMounts:
      - name: config-volume
        mountPath: /etc/config
  volumes:
    - name: config-volume
      configMap:
        name: special-config
        items:
        - key: special.level
          path: keys
  restartPolicy: Never

When the pod runs, the command ("cat /etc/config/keys") produces the output below

very

　　

Project keys to specific paths and file permissions

You can project keys to specific paths and specific permissions on a per-file basis. The Secrets user guide explains the syntax.

Mounted ConfigMaps are updated automatically

When a ConfigMap already being consumed in a volume is updated, projected keys are eventually updated as well.

Kubelet is checking whether the mounted ConfigMap is fresh on every periodic sync.

However, it is using its local ttl-based cache for getting the current value of the ConfigMap. As a result, the total delay from the moment when the ConfigMap is updated to the moment when new keys are projected to the pod can be as long as kubelet sync period + ttl of ConfigMaps cache in kubelet.

Note: A container using a ConfigMap as a subPath volume will not receive ConfigMap updates.

Understanding ConfigMaps and Pods

The ConfigMap API resource stores configuration data as key-value pairs.

The data can be consumed in pods or provide the configurations for system components such as controllers.

ConfigMap is similar to Secrets, but provides a means of working with strings that don’t contain sensitive information.

Users and system components alike can store configuration data in ConfigMap.

Note:

ConfigMaps should reference properties files, not replace them.

Think of the ConfigMap as representing something similar to the Linux /etc directory and its contents.

For example, if you create a Kubernetes Volume from a ConfigMap, each data item in the ConfigMap is represented by an individual file in the volume.

The ConfigMap’s data field contains the configuration data.

can be simple – like individual properties defined using --from-literal –

or complex – like configuration files or JSON blobs defined using --from-file.

kind: ConfigMap
apiVersion: v1
metadata:
  creationTimestamp: 2016-02-18T19:14:38Z
  name: example-config
  namespace: default
data:
  # example of a simple property defined using --from-literal
  example.property.1: hello
  example.property.2: world
  # example of a complex property defined using --from-file
  example.property.file: |-
    property.1=value-1
    property.2=value-2
    property.3=value-3

　　

Restrictions

• You must create a ConfigMap before referencing it in a Pod specification (unless you mark the ConfigMap as “optional”).

  • If you reference a ConfigMap that doesn’t exist, the Pod won’t start.

  • Likewise, references to keys that don’t exist in the ConfigMap will prevent the pod from starting.

• If you use envFrom to define environment variables from ConfigMaps, keys that are considered invalid will be skipped.

  • The pod will be allowed to start, but the invalid names will be recorded in the event log (InvalidVariableNames).

  • The log message lists each skipped key.

   kubectl get events
   LASTSEEN FIRSTSEEN COUNT NAME          KIND  SUBOBJECT  TYPE      REASON                            SOURCE                MESSAGE
   0s       0s        1     dapi-test-pod Pod              Warning   InvalidEnvironmentVariableNames   {kubelet, 127.0.0.1}  Keys [1badkey, 2alsobad] from the EnvFrom configMap default/myconfig were skipped since they are considered invalid environment variable names.　

• ConfigMaps reside in a specific namespace. A ConfigMap can only be referenced by pods residing in the same namespace.

• Kubelet doesn’t support the use of ConfigMaps for pods not found on the API server. This includes pods created via the Kubelet’s –manifest-url flag, –config flag, or the Kubelet REST API.

Note: These are not commonly-used ways to create pods.